Diane Sawyer is stepping down as the anchor of "ABC World News," with David Muir taking over starting on Sept. 2.

In addition, ABC News has promoted George Stephanopoulos to "chief anchor" at the network. He will continue anchoring "Good Morning America" and "This Week," and will officially become the lead anchor on all "major special events and breaking news," per an email sent to staff from ABC News president James Goldston. That includes election night, a role which has traditionally gone to the anchor of the evening newscasts.

Sawyer, the sole female anchor on the network evening newscasts, will assume the "Barbara Walters" role.

"She will create innovative television specials and events, and, of course, continue to conduct the biggest interviews with the most important and extraordinary people in the world," Goldston wrote to staff.

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Late last year there were reports that Sawyer did not want Stephanopoulos to replace her as "World News" anchor, even though he was believed to have a clause in his contract assuring him the role should she step down. Stephanopoulos signed a new deal with ABC News earlier this year. David Muir has long been rumored to be the favorite inside ABC to follow Sawyer, with the New York Post's Richard Johnson reporting in March that Muir would get the top job, but that he would have to wait for Sawyer to step down to do so.

Former ABC News president and the current co-chairman of the Disney-ABC Television Group, Ben Sherwood, made reference to those discussions in an email he sent to ABC News staff.

"Over time, Diane, George and David have each engaged me and James in imagining and charting their respective paths," Sherwood wrote. "We are delighted that these new positions reflect our discussions as well as their individual passions, ideals, talents and goals."

Muir, who for a long time has been viewed as the "next generation" of ABC News anchor, will continue to co-host "20/20" in primetime.